The invention refers to a process for the direct synthesis of fatty amines from esters of fatty acids by the action of ammonia and hydrogen in the presence of mixed dehydration/hydrogenation catalysts; more particularly it is directed to the production, with a high degree of selectivity, of primary amines or dimethylated tertiary amines.
The most used industrial processes for the production of long chain amines; that is to say, those whose molecule contains from 10 to about 24 carbon atoms, are still largely based on the classic reaction of the preparation of the nitrile by reaction of ammonia on the fatty acid and dehydration, followed by hydrogenation of the nitrile thus formed. One thus obtains the long chain primary alkylamine, starting from which one goes over to the dimethylalkylamine by various procedures, of which the oldest known one is doubtlessly the one which is adapted from the Leuckart reaction, and which consists in a dimethylation of the formic acid/formaldehyde system (for instance, U.S. Pat. No. 2,366,534), with the present procedures rather using the reaction of methanol or of formaldehyde in the presence of hydrogen.
Also known are procedures for the obtaining of fatty alkylamines from fatty acids and which proceed in a single stage. They use the reaction of hydrogen and ammonia or low molecular weight amines in the presence of metallic catalysts especially with zinc-chromium or with zinc-aluminum (French Pat. No. 1,549,655), with nickel with various cocatalysts (see, for instance, East German Pat. No. 110,487), or yet based on metallic sulfides (British Pat. No. 1,135,915).
Likewise found described in the prior art are amine fabrication processes using triglycerides as raw material. (German Pat. No. 1,288,595, U.S. Pat. No. 3,579,585). The use of esters as base material for obtaining amines is cited particularly in French Pat. No. 1,598,720, U.S. Pat. No. 2,223,305, and British Pat. No. 421,718, which propose to conduct the amination reaction on mixed catalysts based on zinc or alumina.
The one stage procedures; whether they are based on the acid, the glyceride, or the esters, are evidently of a better industrial advantage than the traditional procedures which necessitate two distinct stages and two distinct catalysts: one for the dehydration into the nitrile, the other one for its hydrogenation, and a transfer of intermediate product. But they also present various drawbacks, among which for those which nevertheless underwent industrial development are the necessity of working at high temperatures and under hydrogen pressures generally above 200 bars, and, above all, of not being selective; that is of delivering, in addition to the alkylamines aimed for, secondary products which it is difficult to eliminate by the usual separation methods, particularly by distillation.